blissfulness vs seventh heaven

blissfulness and seventh heaven both are nouns.

Word	Noun	Adjective	Verb	Adverb
blissfulness	Yes	No	No	No
seventh heaven	Yes	No	No	No

As nouns, blissfulness and seventh heaven are synonyms defined as:

Other synonyms of blissfulness include bliss, cloud nine, walking on air.

blissfulness (noun)	seventh heaven (noun)
a state of extreme happiness	a state of extreme happiness